Electromagnetic horn with moveable vane for generating monopulse radiation patterns

ABSTRACT

An electromagnetic horn with amplitude monopulse radiation patterns has a Magic Tee attached to a waveguide feeding the horn. The Magic Tee provides two signals that have displaced phase centers in the feeding waveguide. Each signal, whose phase center is displaced, provides a radiation pattern whose maximum radiation is angularly skewed from the axis of the horn. A rotationally variable septum provides an angular rotation of both radiation patterns in such a manner as to rotate the reference axis, thereby scanning the monopulse antenna patterns.

iliiited States Patent [191 itiilion et ai.

[ 1 May 15, 11973 [54] ELECTROMAGNETIC IHORN WITH MOVEABLE VANE FOR GENERATING MONOPULSE RADIATION PATTERNS [75] Inventors: Derling G. Killion; Floyd B. Shacklock, both of San Diego, Calif.

[73] Assignee: Ryan Aeronautical Company, San

Diego, Cailif.

22 Filed: July 14,1'969 [21] Appl.No.: 841,357

[52] US. Cl ..343/786, 343/783 [51] Int. Cl. ..H0lq 13/00 [58] Field of Search ..343/776, 778, 786,

[5 6] References Cited UNITED STATES PATENTS 2,415,807 2/1947 Barrow et al .343/786 2,961,659 l 1/1960 Kuecken ..343/786 3,392,395 7/1968 l-lannan ..343/777 3,274,602 9/1966 Randall et al. ..343/755 Primary Examiner -Eli Lieberman Attorney Carl R. Brown 57 ABSTRACT An electromagnetic horn with amplitude monopulse radiation patterns has a Magic Tee attached to a waveguide feeding the horn. The Magic Tee provides two signals that have displaced phase centers in the feeding waveguide. Each signal, whose phase center is displaced, provides a radiation pattern whose maximum radiation is angularly skewed from the axis of the horn. A rotationally variable septum provides an angular rotation of both radiation patterns in such a manner as to rotate the reference axis, thereby scanning the monopulse antenna patterns.

6 Claims, 8 Drawing Figures l 1 ELECTROMAGNETIC HORN WITH MOVEABLE VANE FOR GENERATING MONOPULSE RADIATION PATTERNS BACKGROUND OF THE INVENTION In amplitude monopulse radiating systems, it is necessary to provide radiation patterns that are rotationally skewed from each other. The axis on which the radiation patterns cross each other provides a reference axis to which antennas, missiles, or other devices can be aligned, thereby providing automatically controlled guidance for tracking systems. In known systems employing horns, the radiation pattern is skewed from the axis by physically pointing two horns in the desired direction. In this arrangement, one horn is pointed at a few degrees angle to the other horn. Thus such a system requires two horns and sufficient space to contain the two horns. If the antenna is to be scanned over large rotational angles the reference axis must have its angular position changed also. This is presently done by mechanically rotating the two antennas.

Thus it would be advantageous to have a single horn 4 that is capable of providing scanning monopulse radiation or antenna patterns.

SUMMARY OF .THE INVENTION In an embodiment of this invention, one electromagnetic horn is fed through a short length of waveguide by a Magic Tee hybrid. The angular position of the in dividual beam maximums is altered by displacing the phase center of the hybrid signals from the horn axis.

In this manner, the position of the reference axis as well ble of providing scanning type monopulse radiation patterns. Other objects and many advantages of this invention will become more apparent upon a reading of the following detailed description and an examination of the drawings wherein like reference numerals designate,

like parts throughout and in which:

FIG. 7 is a schematic diagram of the waveforms of the hybrid signals rotationally skewed by movement of the rotationally variable septum.

FIG. 8 is a schematic diagram of the waveforms of the sum and difference waveform pattern information received by the electromagnetic horn of this invention when the septum is rotationally moved.

Referring now to FIG. 1, a horn type electromagnetic antenna 10 has a flared horn 12, the outer end of which forms a horn aperture. The horn is connected at 27 to a section of waveguide in which is positioned a Magic Tee hybrid unit 22. Connected to the section of waveguide is an input or output section 18 and an input or output port 16. In use of the antenna as a receiver, output section 18 is the sum output and port 16 is the difference output. g

It may be understood that the portion of the waveguide section 14, that is inclusive of the plate element 22 and the output section 18 and port 16, comprises a folded Magic Tee hybrid unit. This unit is sometimes called a monopulse comparator or a 180 hybrid unit. Positioned in the section of waveguide between the folded Magic Tee hybrid unit and the horn 12 is a septum plate 24 having a moving vane 20 that pivots on axle members 26. The plate 22 and the septum 24 extend from and are secured to the opposite sides of the outer housing structure and divides equally the volume in the waveguide section and the Magic Tee hybrid unit. The end of the moving vane generally moves in an arc along dotted line 30, see FIG. 3, that corresponds to the point of joining the waveguide section with the horn 12. Thus upon movement of the moving vane 20,

the cross sectional area of the gap in each side of the waveguide section is selectively reduced or increased in size as illustrated in FIG. 3. The moving vane 20 can be rotated by any known suitable mechanism being attached to the axle members 26.

In operation, the antenna performs the same whether the electromagnetic horn is used in a transmitting or receiving mode. Accordingly, the operation will be described first in the transmitting mode. A signal is supplied to the folded Magic Tee hybrid unit that provides two signals, one in each of the passages, that have dis- FIG. 1 is an end view in perspective of an embodi- I ment of the invention.

FIG. 2 is an end plan view of an embodiment of the invention.

FIG. 3 is a cross sectional view taken along lines 3-3 of FIG. 2. I

FIG. 4 is a cross sectional view taken along lines 4-4 of FIG. 2.

FIG. 5 is a schematic diagram of the waveforms of a hybrid signal before and after movement of the rotationally variable septum in reducing the volume of the cavity passing the signal to the horn.

FIG. 6 is a schematic diagram of the waveforms of a hybrid signal before and after movement of the rotationally variable septum in enlarging the volume of the cavity passing the signal to the horn.

placed phase centers. At the dotted line 30, with the moving vane 20 in the center or along the axis of the waveguid and horn, the hybrid signals have the phase and amplitude through spaces 32 and 34 that correspond respectively to waveform 46 in FIG. 5 and waveform 50 in FIG. 6. With the moving vane 20 pivoted,

as indicated in FIG. 3, in the counter clockwise direction, the area or gap at 32 narrows displacing the phase center of the hybrid signals to the right in FIGS. 5 and 6. With reference to FIG. 5, the waveform of the hybrid signal 46 as a result of the narrowing of the gap 32, decreases in amplitude to waveform 44 with an amplitude peak at 48 that is shifted in phase from peak 46. The same applies to the phase center of the hybridsignal in the enlarged gap 34 wherein the waveform 50 is increased in amplitude to waveform 52 and the peak of the waveform at 54 is advanced in phase to the peak point 56. Accordingly, from the illustrations in FIGS. 5 and 6, it may be observed that the Magic Tee hybrid unit displaces the phase centers of the two hybrid signals to provide peak amplitude points at 46 and 56 providing a zero difference line at center line 40, that corresponds to a zero degree angular skewing or rotation of the radiation patterns. Upon moving vane 20 in a counter clockwise direction, the respective waveforms 44 and 52, illustrated in FIG. 7, provides an intersecting beam at 48 that corresponds with the center line along the composite amplitude phase center of the two modified hybrid signals. Accordingly, the radiation pattern has advanced in phase to 6 and the radiation patterns have been rotated in a clockwise direction.

The previous description also applies if the moving vane 20 is moved to restrict the gap 34 and enlarge the gap 32. For a clockwise rotation of the moving vane, the radiation pattern rotates or skews in a counter clockwise direction.

The Magic Tee unit also takes the signals at gaps 32 and 34 in the receiving mode and combines them as a monopulse pattern by adding the waveforms 44 and 52. This provides the sum signal 70 in the output vane 18 and the difference signal 72 in port 16. Since the difference signal 72 has a zero amplitude at this angle corresponds with the clockwise skewing of the radiation or antenna scanning pattern as previously described.

Having described our invention, we now claim.

1. An electromagnetic horn for providing amplitude monopulse radiation patterns comprising,

an electromagnetic born,

a waveguide section connected to said horn for providing two hybrid signals that have displaced phase centers in said waveguide section,

means in said waveguide section for displacing the phase center of the composite hybrid signals from the horn axis to change the angular positin of the radiation or scanning pattern of the horn,

said means for providing said two hybrid signals comprises a Magic Tee positioned in said waveguide section,

a sum output opening and a difference port connected to the end of said waveguide section opposite to the end connection to said horn,

said Magic Tee comprising an elongated plate that separates a portion of the longitudinal volume of said waveguide section into two equal passage openings having equal cross sectional areas,

means for displacing the phase center including plate means for selectively reducing the cross sectional area of one of said passage openings adjacent the connection of said waveguide section to said horn.

2. An electromagnetic horn as claimed in claim 1 in which,

said plate means comprises a pivoting vane that pivots on an axis parallel to said elongated plate.

3. An electromagnetic horn as claimed in claim 2 in which,

said pivot axis is in the same plane as said elongated plate.

4. An electromagnetic horn as claimed in claim 3 in which,

a second elongated plate is positioned between said elongated plate and said pivoting vane, which second plate is in the plane of said elongated plate and is spaced therefrom.

5. An electromagnetic horn as claimed in claim 2 in which,

the moving end of said pivoting vane is positioned at substantially the intersection of said waveguide section and said horn.

6. An electromagnetic horn as claimed in claim 5 in which,

one end of said elongated plate is posiioned adjacent said sum output opening and said difference port. 

1. An electromagnetic horn for providing amplitude monopulse radiation patterns comprising, an electromagnetic horn, a waveguide section connected to said horn for providing two hybrid signals that have displaced phase centers in said waveguide section, means in said waveguide section for displacing the phase center of the composite hybrid signals from the horn axis to change the angular positin of the radiation or scanning pattern of the horn, said means for providing said two hybrid signals comprises a Magic Tee positioned in said waveguide section, a sum output opening and a difference port connected to the end of said waveguide section opposite to the end connection to said horn, said Magic Tee comprising an elongated plate that separates a portion of the longitudinal volume of said waveguide section into two equal passage openings having equal cross sectional areas, means for displacing the phase center including plate means for selectively reducing the cross sectional area of one of said passage openings adjacent the connection of said waveguide section to said horn.
 2. An electromagnetic horn as claimed in claim 1 in which, said plate means comprises a pivoting vane that pivots on an axis parallel to said elongated plate.
 3. An electromagnetic horn as claimed in claim 2 in which, said pivot axis is in the same plane as said elongated plate.
 4. An electromagnetic horn as claimed in claim 3 in which, a second elongated plate is positioned between said elongated plate and said pivoting vane, which second plate is in the plane of said elongated plate and is spaced therefrom.
 5. An electromagnetic horn as claimed in claim 2 in which, the moving end of said pivoting vane is positioned at substantially the intersection of said waveguide section and said horn.
 6. An electromagnetic horn as claimed in claim 5 in which, one end of said elongated plate is posiioned adjacent said sum output opening and said difference port. 